Brushless type rotation detectors such as brushless resolvers or brushless synchros transmit signals using a rotation transformer constituted by a stator transformer and a rotor transformer instead of a brush.
FIG. 5 is a half section showing a structure for a brushless resolver as an example of a conventional brushless type rotation detector. In the figure, the conventional brushless resolver includes a signal modulation section (constituted by 51 and 52, or the like described later) for modulating an output voltage induced by an excitation voltage according to a rotation angle to be detected, and a case 55 that houses the signal modulation section, and the signal modulation section includes a rotor iron core 51, a stator iron core 52, a rotor transformer 53, and a stator transformer 54, around each of which a coil is wound. Conventional resolvers including such a structure are disclosed in FIG. 2 of the invention of “a resolver” disclosed in Japanese Patent Laid-Open No. 11-322662 (the entire document and FIG. 2), and many other patent documents.